Street-fighting man still packs a real punch

One-time boxing champion Johnny Harris has become a Brit-flick star

After half a lifetime of fighting and boozing, sleeping rough and trying to end it all, Johnny Harris can finally stop running away.

One of Britain's finest and toughest actors is working with his heroes at last.

In getting to this position he has taken on some of the most unsavoury roles imaginable – rapists, pimps and thugs – playing the parts with a disarming realism that could surely only be achieved by someone who has been face to face with their own demons.

Sitting in the sunshine outside a Soho café, he is welling over with gratitude for his new life. There's no sign here of Mick, the hate-filled serial sex abuser from Shane Meadows's This Is England '86. Yet so menacing was Harris's performance that he was nominated as best supporting actor in this year's Baftas. He played a similarly flawed character, a pimp called Derek, in the cult film London to Brighton, and is starring in the fantasy horror The Fades on BBC3.

Only a few years after being homeless, he finds himself working on two major feature films. Welcome to the Punch sees him in another gangster role, appearing with James McAvoy and Mark Strong in a fast-moving depiction of the London underworld, which will give an alternative view of the capital in Olympics year. In Snow White and the Huntsman, Harris, 37, will play one of the dwarfs, alongside Ray Winstone, Bob Hoskins and Ian McShane.

At the age of nine, Harris joined Fitzroy Lodge boxing club, near his home in Lambeth, south London, as a refuge from the classroom. "I found a little secret world," he recalls. By the time he was 13, he had abandoned school altogether.

By the age of 16, he had won the national Amateur Boxing Association title at light flyweight. "Everyone was celebrating but I remember thinking that it wasn't the answer. I felt like a bit of a fraud." So he ran away again, this time to Paris before heading back to London determined to take his place in the pantheon of British acting. He enrolled in acting classes at Morley College, south London, and embarked on a career in local underground playhouses such as the White Bear and the Union Theatre. "I wanted to be one of the great actors. Gary Oldman's Nil by Mouth had made a great impact on me – I lived on the estate where they made that film. I started realising that Michael Caine, Charlie Chaplin had all come from where I had come from."

Finally, he was spotted in a fringe play and cast in Paul McGuigan's stylish movie Gangster No 1. But when more success did not come, Harris hit the booze even harder, turned his back on his friends and made his home on the streets. "I had a breakdown," he says. Four and a half years ago, Harris came off the bottle and his life changed. Shortly afterwards he was, to his surprise, recognised in the street by the actor Martin Freeman, who praised his role in London to Brighton. The meeting encouraged Harris to turn down a mediocre part he had been planning to accept – and almost immediately came the call from Shane Meadows. The angry, scary parts are flooding in but the actor himself, who is getting married next year, has discovered a new calm. "I've started to find tolerance and be less self-obsessed," he says. But isn't he afraid he will no longer be able to play the nasty roles for which he is known? "Oh, the anger is there, it's always there, but I think every human being has fear of abandonment and rejection and failure," he says. "I've certainly got access to those things at the flick of a button."

'Welcome to the Punch' and 'Snow White and the Huntsman' are due out in 2012